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Designed by Dr. Claudius Dornier, the Dornier Do-X was the largest and heaviest flying boat in the world upon its completion in 1929, with a wingspan of 157 feet and a maximum takeoff weight of more than 61 tons.

The massive aircraft was financed by the German Transport Ministry, but it was built in Switzerland, on the shores of Lake Constance, in order to comply with terms of the Treaty of Versailles, which forbade Germany from building certain classes of aircraft.

The Do-X was powered by a dozen engines mounted in a tandem “push-pull” configuration atop the wing, which could just barely haul the hulking craft up to an altitude of 1,650 feet. True to its boat-like design, the Do-X's complex engines were not directly controlled by the pilot — the captain in the cockpit had to send orders for throttle adjustments to a flight engineer in the engine room.

July 9, 1929

A completed Dornier Do-X flying boat in the assembly hangar of the aircraft plant in Altenrhein, Switzerland before her maiden flight.

Image: ullstein bild/ullstein bild via Getty Images

July 9, 1929

A completed Dornier Do-X flying boat in the assembly hangar of the aircraft plant in Altenrhein, Switzerland.

Image: ullstein bild/ullstein bild via Getty Images

July 25, 1929

A machinist in the flying boat's engine room.

Image: ullstein bild/ullstein bild via Getty Images

Oct. 21, 1929

Image: ullstein bild/ullstein bild via Getty Images

Oct. 21, 1929

A machinist in the engine room of the flying boat.

Image: ullstein bild/ullstein bild via Getty Images

Accommodations aboard the Do-X were spacious and luxurious, with a dining salon, smoking lounge, wet bar and comfortable seating for 70 to 100 passengers.

The Do-X made its first test flight on July 12, 1929. A few months later, it carried a world-record 169 passengers on a 40-minute flight. Passengers were asked to move from one side of the cabin to the other to help the captain bank into turns.

In 1930, the Do-X took off on an international publicity tour, hopping through Europe, down the west coast of Africa, across the Atlantic to Brazil and up to New York before returning to Berlin.

The tour was intended to stoke interest in the Do-X for civilian air travel, but apart from two additional models built for the Italian state airline SANA, the leviathan of the sky failed to take off commercially.

Oct. 21, 1929

Dornier employees and crew staff aboard the Dornier Do-X on a flight over Lake Constance, Germany.

Image: ullstein bild/ullstein bild via Getty Images

Oct. 21, 1929

Image: ullstein bild/ullstein bild via Getty Images

1930

The flying boat arrives in England.

Image: Keystone-France/Gamma-Keystone via Getty Images

1930

Image: ullstein bild/ullstein bild via Getty Images

Sept. 18, 1930

An operator tests the radio reception in the lounge of the flying boat.